A feed-through (or feed-thru) is a device used to enable communication of some sort through a bulkhead, such as a housing of an electronic module. Any feed-through has a body portion adapted to be secured in an opening formed in the bulkhead, and the body portion is provided with one or more through-holes that define communication paths through the bulkhead. The communication may be physical (pneumatic, liquid, gaseous or mechanical, for example), optical or electrical. In electrical applications, for example, each through-hole accommodates an electrical wire, and the space between each wire and the inside diameter of the respective through-hole is filled with a non-conductive sealant to electrically insulate the wire from the body portion and to provide an environmental seal. If a hermetic seal is required, the sealant may be a glass or ceramic composition, such as shown in the U.S. Pat. No. 5,650,759 to Hittman et al., issued on Jul. 22, 1997. In other applications, an epoxy or thermosetting plastic material may be used as a sealant, such as shown and described in the U.S. Pat. No. 6,453,551 to Nordquist et al. Many electrical feed-throughs also include a filter component such as a ceramic capacitor which is soldered to the wire and the body portion to provide electrical noise suppression in signals carried by the wire. Other filter elements such as inductors and/or resistors may also be incorporated into the body portion to form various well-known filter topologies.
While soldering or threading has traditionally been used to secure feed-through devices in the bulkhead opening, press-in feed-through devices have gained popularity, particularly in electrical applications where the bulkhead material is typically a relatively soft metal such as aluminum or zinc. FIGS. 1A and 1B depict a representative prior art press-in electrical feed-through device 10 having a cylindrical body portion 12 formed of a material significantly harder than the typical bulkhead material. An electrical wire 14 passes through a through-hole 16 formed in the body 12, and a sealant 18 fills the space in through-hole 16 around the wire 14. The body portion 12 includes an inboard end 12a that centers the feed-through 10 in the bulkhead opening, a circumferentially knurled portion 12b providing an interference fit between the feed-through 10 and the bulkhead opening, and a flange 12c for limiting the depth of insertion. When the feed-through 10 is pressed into the bulkhead opening, the knurls 12b gall or plow into the bulkhead material, and insertion forces on the order of several hundred pounds are commonly required. This not only gouges and work-hardens the bulkhead material, but also exerts very high radially compressive forces on the periphery of the body portion 12. The compressive forces are of particular concern because they tend to flex the body portion 12, and can crack solder joints and ceramic sealants and components of the feed-through 10. In cases where such a failure occurs, the defective feed-through 10 can be removed, but it is difficult to securely seat a replacement feed-through device in the same bulkhead opening due to the prior gouging and work-hardening of the surrounding bulkhead material. Accordingly, what is needed is an improved press-fit feed-through device that can be inserted with lower force, and that is less susceptible to failure due to compressive loading during insertion.